1. Field of the Invention
This invention relates to the field of water treatment, and more particularly to the purification or sterilization of contaminated water using halogens, e.g., iodine and bromine. More specifically, the invention relates to methods and apparatus for the stepwise treatment of water for human or animal consumption perferably using iodine and the removal of the iodine to levels below that detectable by human taste or smell.
2. Description of the Prior Art
It has long been known that elemental iodine possesses bactericidal, viricidal and cysticidal properties and that because of this biocidal action, it is ideal for use as a water purifying agent. U.S. Pat. No. 3,408,295 discloses a method of purifying water for drinking purposes utilizing elemental iodine. However it is also known that the use of iodine in the purification of drinking water is not widely used because, although sterile, the water has an objectionable odor, color and taste due to the iodine present. As a practical matter, the use of iodine to provide sterilized or purified drinking water is used only in emergency situations or where there is no other alternative available. To meet the requirements of potable water which also has acceptable taste, the iodine remaining after the treatment must be removed.
U.S. Pat. No. 4,367,149 discloses a method of removing this elemental iodine by the reaction of sodium or potassium thiosulfate. However, although the iodine is removed, there is left in its place other inorganic salts such as sodium iodide. Furthermore, unless the exact stoichiometric amount of thiosulfate is used, either some iodine or the excess thiosulfate will be present. Other chemical methods for removal of the elemental iodine from the treated water have been proposed.
What is needed is a complexing agent, harmless to humans, which will act as a scavenging agent removing all the iodine but leaving nothing in its place. It is therefore an object of this invention to provide process and apparatus using a complexing agent which will quickly and completely remove all traces of iodine after its biocidal action has rendered the water safe for human and animal consumption.
It is also an object of this invention to provide a simple and economical method and apparatus for purifying and sterilizing water employing iodine or bromine which results in potable water which contains none of the characteristic taste or color of the elemental halogen employed as the biocidal agent.
It is a further object of this invention to provide a method as described above which can be practiced in either a batch or a continuous fashion.
It is another object of this invention to provide a method and apparatus in which the material employed to remove the halogen biocidal agent can be reactivated and reused repeatedly without loss in effectiveness.